refactor: 移除 Python 后端源码，全面迁移至 Rust gateway 架构

- 删除全部 Python 源码 (src/) 及 Alembic 迁移脚本，归档至 _deprecated_py_src/
- 重构 Rust gateway ai_pipeline: 拆分 planner/finalize 模块，新增 contracts/adaptation 层
- 重组 handlers 模块为 admin/public/proxy/internal/shared 子模块结构
- 新增 executor 模块，引入 Rust 原生数据库迁移 (aether-data/migrations)
- 简化 CI/Docker 构建流程，移除 base image 二级构建，统一为单一 app image
- 移除 Python 相关基础设施文件 (entrypoint.sh, gunicorn_conf.py, Dockerfile.base)

_deprecated_py_src/services/task/submit/attempt.py

@@ -0,0 +1,75 @@
+from __future__ import annotations
+
+from collections.abc import Callable
+from typing import Any
+
+import httpx
+from sqlalchemy.orm import Session
+
+from src.services.billing.rule_service import BillingRuleLookupResult
+from src.services.candidate.submit import SubmitOutcome
+from src.services.task.submit.record import AsyncSubmitRecordService
+from src.services.task.submit.response import AsyncSubmitResponseService
+
+
+class AsyncSubmitAttemptService:
+    """异步提交单候选执行编排服务。"""
+
+    def __init__(
+        self,
+        db: Session,
+        *,
+        sanitize: Callable[[str], str],
+        extract_response_text: Callable[[httpx.Response], str],
+        match_provider_failover_rule: Callable[..., str | None],
+    ) -> None:
+        self.db = db
+        self._record_ops = AsyncSubmitRecordService(db)
+        self._response_ops = AsyncSubmitResponseService(
+            db,
+            record_ops=self._record_ops,
+            sanitize=sanitize,
+            extract_response_text=extract_response_text,
+            match_provider_failover_rule=match_provider_failover_rule,
+        )
+
+    async def submit_candidate(
+        self,
+        *,
+        candidate: Any,
+        record_id: str | None,
+        candidate_info: dict[str, Any],
+        candidate_keys: list[dict[str, Any]],
+        rule_lookup: BillingRuleLookupResult | None,
+        submit_func: Any,
+        extract_external_task_id: Any,
+    ) -> tuple[SubmitOutcome | None, int | None]:
+        self._record_ops.mark_pending(record_id=record_id)
+
+        # Flush/commit BEFORE awaiting upstream submit to avoid holding DB connections.
+        if self.db.in_transaction():
+            try:
+                self.db.commit()
+            except Exception:
+                self.db.rollback()
+                raise
+
+        # Attempt submit (upstream HTTP)
+        try:
+            response: httpx.Response = await submit_func(candidate)
+        except Exception as exc:
+            return self._response_ops.handle_submit_exception(
+                record_id=record_id,
+                candidate_info=candidate_info,
+                exc=exc,
+            )
+
+        return self._response_ops.handle_submit_response(
+            candidate=candidate,
+            record_id=record_id,
+            candidate_info=candidate_info,
+            candidate_keys=candidate_keys,
+            rule_lookup=rule_lookup,
+            response=response,
+            extract_external_task_id=extract_external_task_id,
+        )